Integrated circuits such as computer chips are manufactured from semiconductor wafers. These wafers are subjected to numerous steps during the process of making integrated circuits. This generally entails transporting a plurality of wafers from one workstation to another for processing by specialized equipment. As part of the processing procedure, wafers may be temporarily stored or shipped in containers to other plants or to end users. Such intra-facility and extra-facility movements may generate or expose the wafers to potential wafer ruining contaminants. In order to reduce the deleterious effect of contaminants on wafers, specialized containers have been developed to minimize the generation of contaminants and to isolate wafers from contaminants exterior to the containers. A principal feature common to these containers is that they are provided with supporting structures to support the wafers inside.
Plastic containers have been used for decades for transporting and storing wafers in-between process steps. Such containers have highly controlled tolerances for interfacing with processing equipment as well as the equipment/robots that transport the containers. Moreover, it is desirable in such plastic containers to use components that are attachable and removable without using metallic fasteners such as screws, since metal fasteners can cause particle generation when inserted and removed.
Additional, required or desirable characteristics of containers to transport and/or store semiconductor wafers include light weight, rigidity, cleanliness, limited gaseous emissions, and cost effective manufacturability. The containers provide hermetic or close to hermetic isolation of wafers when the containers are closed. Simply stated, such containers need to keep the wafers clean, uncontaminated, and undamaged. Additionally, carriers need to maintain their capabilities under the rigors of robotic handling which includes lifting the carrier by the robotic flange positioned at the top of the container. Further, carriers may be subject to shock from any direction when in transit as well as being subject to changes in orientation when in transit.
Front opening wafer containers have become the industry standard for transporting and storing large diameter 300 mm wafers. In such, containers the front door is latchable within a door frame of a container portion, and closes a front access opening through which the wafers are robotically inserted and removed. When the container is fully loaded with wafers the door is inserted into the door frame of the container portion and latched thereto. The enclosure portion generally includes a top wall, a bottom wall, side walls, a back wall, and a door frame defining a front opening.
The semiconductor industry is now moving toward using even larger 450 mm diameter wafers. The larger diameter wafers, although providing cost efficiencies, also provide increased fragility, greater weight, and present undiscovered issues associated with handling and storing the larger wafers in containers made of plastic. Deflection and related problems associated with the expanses of plastic on the top, bottom, sides, front, and back are exacerbated. When the carrier door seats and engages the receiving frame of the carrier shell, the door cushion pushes the wafer against a rigid surface or backstop that is located near the rear of the carrier shell. In a carrier, such as a FOUP, used for the transport of wafers in a FAB facility, one of the reasons for alignment with the backstop is to accurately position the wafer radially. This raises several concerns. First, in cases where the wafer retention forces applied by the door cushion are large, contact stresses between the wafer and the backstop can permanently deform the backstop surface. Second, over time, the wafer backstop will wear due to contact with the wafer during carrier transport. The wear can occur due to ordinary transport operation or under conditions of excessive transport vibration. Third, to minimize the above two problems, it may be required for the backstop to be manufactured from a different material than the wafer support. Although a design for a replaceable backstop exists wherein a backstop component is attached to the rear interior wall of the carrier shell, this arrangement tends to cause the wafer position to be inaccurate due to the location of the wafer backstop contact surfaces relative to the center axis of the wafer.
A wafer carrier used for shipping wafers, such as a FOSB or MAC generally includes wafer supports that lift the wafers during wafer shipment. If the wafer shipping carrier is then repurposed for use in a FAB, it is no longer desirable for the wafer to be stored in a lifted position.
There are several drawbacks associated with prior wafer handling devices or containers related to these issues. In one prior art approach, the wafer backstop is integrated into wafer support. Therefore, the backstop is made from the same material as the wafer support. The wafer support is comprised of a low wear, rigid material. Although the wafer support is designed to endure the contact stresses generated by the retention of the wafer, the backstop will wear over time due to forces normally generated during transport.
In another prior art approach, the wafer backstop is overmolded onto the wafer support and is a different material than the wafer support. The overmolded material has high wear resistance and is rigid. Here, although the wafer support backstop is designed to endure the contact stresses generated by the retention of the wafer, the backstop will still wear over time due to forces typically generated during transport.
Accordingly, a need in the industry exists for a wafer container that addresses one or more of these problems, particularly as they exist relative to containers for 450 mm diameter and larger wafers.